Processes and apparatus are known from U.S. Pat. No. 4,941,093 with which a defined ablation of surfaces is possible. In particular, processes and apparatus are described in this patent that make possible a defined ablation of the cornea. The optical properties of the cornea are to be modified in this manner such that errors of vision such as hyperopia or myopia can be corrected. This is effected in that the beam cross section of a laser beam which impinges on the cornea is modified in shape and size in the course of time such that a cumulative ablation effect on the affected surface results in the desired new surface profile. The processes described in this patent provide a variation during the course of time, in succession from initially larger affected surfaces of varied shapes towards smaller affected surfaces, or vice versa. In such processes, the radiation source used, i.e., a laser, must be designed such that a sufficient energy density over the whole beam cross section is available for even the largest affected surface. For the laser system used, and in particular for the proposed excimer laser, there is an immense apparatus cost as soon as it is desired to process large surfaces with it.
Furthermore, it is known from DD-Patentschrift (East German patent) 263,447 to make use of an axicon pair in combination with a cylindrical lens array in order to reduce the technical equipment cost in the operative treatment of the cornea. This arrangement is however primarily suitable for the positioning of cut patterns in the cornea, i.e., less suitable for the ablation of surfaces.